http://www.la12.org/articles/commotio_cordis.htm
"Commotio Cordis is a syndrome that results from a blunt impact to the chest which leads to cardiac arrest. It is a poorly recognized and underreported event that happens to healthy young athletes as a result of a low-energy, non-penetrating blow to the chest. Commotio Cordis does not result solely from the force of a blow. It is largely the result of the exquisite timing of the blow during a narrow window within the repolarization phase of the cardiac cycle, 15 to 30 msec prior to the peak of the Twave.

Young athletes are especially at risk because of the pliability of their chest walls. Athletes wearing chest protectors have died while playing baseball, lacrosse, hockey and softball. 75 cases have been well documented since the formation of the United States Commotio Cordis Registry (Minneapolis, MN) three years ago. The true number of deaths is unknown because of underreporting and misclassification."

http://jama.ama-assn.org/issues/v287n9/abs/joc11253.html

http://www.nemc.org/medicine/card/commotiocordis.htm

http://www.nemc.org/medicine/card/commotiocordis.htm

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Hard work, Patience, Dedication.
The more you sweat in training, the less you bleed later.

"I get hit moderately hard in the chest pretty much every practice."
then you are fine :)

from
http://news.bbc.co.uk/1/hi/health/1854471.stm

"Most commotio cordis impacts, according to the authors, are of low-energy and velocity and involve a solid core projectile such as a baseball or ice hockey puck. "

--
Hard work, Patience, Dedication.
The more you sweat in training, the less you bleed later.

You're probably right, thanks.

One reason the article caught my attention, though, is because on a couple of occasions I've been hit hard enough in the chest to cause a change in rhythm via extra heartbeats (I think they are called ectopic or some such term). I checked with a doctor and he said that extra beats (which I sometimes get at random) are no cause for concern. Still, no one likes to feel their heart rhythm change. I've practiced with guys (none lately) that wouldn't let you punch them in the chest (even lightly as to demonstrate a technique), and always kind of thought they were annoying and useless to train with. Maybe they just have had similar thoughts and experiences.

"One reason the article caught my attention, though, is because on a couple of occasions I've been hit hard enough in the chest to cause a change in rhythm via extra heartbeats (I think they are called ectopic or some such term). "
wow, haven't experianced that but i've had my thinking process slowed a bit lol

"Maybe they just have had similar thoughts and experiences."
experiances? lol, well the chance is rare, i'll take my chances and get hit

--
Hard work, Patience, Dedication.
The more you sweat in training, the less you bleed later.

I've had the wind knocked out of me a couple times real bad. I've only had once though that someone has actually hit me hard enough and just right to experience a heart skip type feeling. It was a TKD sparring partner, his dad was a boxer, so he knew how to punch, and it was even through a chest protector. I had to sit out the rest of class because I felt like I was going to black out and the next day I had a giant bruise on my chest. Not too fun. Thanks David.

"I think, in one of the episodes of ER, there was this case of little kid who suffered a cardiatric arrest because he got kicked in chest lightly."
according to the sites i've read, 11-13 year olds are most in danger of this.....

"It was a TKD sparring partner, his dad was a boxer, so he knew how to punch, and it was even through a chest protector."
ouchy,

--
Hard work, Patience, Dedication.
The more you sweat in training, the less you bleed later.